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Mineral and Rock Resources Mineral Resources • Backbone of modern societies • Availability of mineral resources as a measure of the wealth of a society • Important in people’s daily life as well as in overall economy • Processed materials from minerals accounting for 5 percent of the U.S. GDP – Value of domestic minerals ~454 billion – Value of domestic reclaimed minerals ~9.3 billion – Value added by major industries (including manufacture of durable goods)that use processed mineral materials ~1.9 trillion • Mineral resources are nonrenewable • Mineral resources: Usable economic commodity (profitable) extracted from naturally formed material (elements, compounds, minerals, or rocks) • Reserve: Portion of a resource that is identified and currently available to be extracted legally Types of Mineral Resources • Based on how we use them – Materials for metal production and technology – Construction materials – Agricultural industry (fertilizers) – Mineral resources for chemical industry – Others (precious gem stones, cosmetics, food, etc.) – Energy mineral resources Mineral Resource Problems • Nonrenewable resources • Finite amount of mineral resources and growing demands of the resources • Supply shortage due to the growing global industrialization, with more developed countries consuming disproportionate share of mineral resources • The erratic distribution of the resources and uneven consumption of the resources – Highly developed countries use the most of the resources Responses to Limited Availability • • • • Find more sources Find a substitute Recycle Use less and make more efficient use of what is available • Do without Classification of Mineral Resources • Based on geologic process of formation – Igneous – Metamorphic – Sedimentary – Biologic – Weathering Igneous Processes • Crystal Settling – As magma cools, heavy minerals that crystallize early may settle to bottom of magma chamber – Example: Chromite (ore of chromium) • Late Magmatic Process – Occur toward the end of crystallization – Heavy metals in water solution is squeezed into fractures • Hydrothermal replacement – Originate from late stage magmatic processes – Mineralizing fluids that migrate through a host rock, crystallizing as veins – Sources for gold, silver, copper, mercury, lead and other resources Metamorphic Processes • Contact – Metamorphism in response to the heat provided by a nearby magma body • Regional – Large areas subjected to intense pressure Metamorphic Processes • Contact – Ore deposits are often found along the contact between the igneous rock and the rocks they intrude upon – The width of the metamorphosed zone depends on the nature of the host rock Contact Metamorphism Metamorphic Processes • Regional – Possible source of some hydrothermal fluids – May form in high temperature, high pressure zones, where fluids may be produced and forced into nearby cavities Igneous and Metamorphic Processes • In addition to producing ore deposits, these processes also produce stone that has economic viability – – – – – Granite Basalt Marble Slate Quartzite • In total value, with the exception of iron and steel, the stone industry is the largest nonfuel mineral industries Sedimentary Processes • Sand and Gravel – Wind and running water help segregate sediments by size, shape, and density – Best deposits are those in which finer sediments have been removed by water or wind – US sand and gravel industry amounted to approximately $7 billion – Most sand and gravel are obtained from river and glacial deposits – Shortages expected with restrictions on land zoning and extraction – Environmental degradation can occur and objections are becoming common Sedimentary Processes • Placer Deposits – If the bedrock in a river basin contains heavy metals (including gold), streams draining the basin may concentrate these heavy metals to form placer deposits – Helped stimulate settlement in the western US Sedimentary Processes • Evaporite Deposits – Widely used in industry and agriculture – Can be grouped into three types • Marine • Nonmarine • Brines – Some beds are compressed by overlying rock layers to form salt domes • Good source for nearly pure salt • Oil deposits can be found on their flanks Salt Dome Evaporite Deposits Biologic Processes • Organisms can produce many types of valuable minerals • Phosphate deposits consist of phosphorous-rich rocks which include bones and teeth (the mineral apatite) – Large phosphate deposits are found in “Bone Valley” in western Florida – Consists largely of fossils of marine organisms – Have supplied up to 1/3 of the world’s phosphorous production Bone Valley Weathering Processes • Residual Ore Deposits – Intensive weathering of rocks can produce deposits of less soluble materials – Laterites – a residual soil derived from Al-rich and Fe-rich igneous rocks – The weathering process concentrates insoluble Al and Fe oxides – If sufficiently concentrated, bauxite can form Weathering Processes • Secondary Enrichment – Near the surface, primary ores (iron, copper, silver) is in contact with slightly acidic soil water – As they ores are dissolved, they migrate downward toward the water table – Below the water table, the solutions may be deposited as sulfides (which are much higher in concentration than near the surface) Minerals from the Sea • Sulfide deposits – Massive sulfide deposits containing zinc, copper, iron, and trace amounts of silver are produced at the black smokers along the oceanic ridges, from which the hot, darkcolored, mineral-rich water emerges as hot springs • Manganese nodules – cover vast areas of the deep-ocean floor (up to 50 percent in certain area), containing manganese (24 percent) and iron (14 percent), with secondary copper (1 percent), nickel (1 percent), and cobalt (0.25 percent). Most abundant in where sediment is at a minimum, generally at depths of 5 to 7 km Environmental Impact from Mineral Development • The impact depends upon many factors – Mining procedures – Hydrologic conditions – Climate factors – Types of rocks and soils – Topography Environmental Impact from Mineral Development • Mineral exploration and testing – Surface mapping, geochemical, geophysical, and remote-sensing data collection – Test drilling • Impact – Generally minimal impact – More planning and care needed for sensitive areas (arid, wetlands, and permafrost areas Environmental Impact from Mineral Development • Mineral Extraction and Processing – Direct impact on the land, water bodies, air quality – Indirect impact on topography of the landscape, transportation of materials – Social impact by creating a need for increased housing and services Environmental Impact from Mineral Development • Minimizing environmental degradation canbe difficult because as the demand for more minerals increases, exploitable deposits are decreasing • Thus, mining operations have to increase to meet demand • Environmental degradation can extend beyond the borders of the mine; the impact of a single mine can have far reaching consequences Mine Wastes • Approximately 60% of land dedicated to mining is used for extraction • The remaining 40% is used for waste disposal • Most waste is overburden – rock removed to get to the ore • Represents 40% of all solid waste generated in the US Types of Mining • Surface mining is more economical but has a greater environmental impact Surface Mining • More common • Less expensive • Overburden must be removed – Soil and vegetation • There are two kinds of surface mining – Open-pit surface mining • A giant hole is dug to extract minerals – Strip mining • A trench is dug to extract the minerals Subsurface Mining • • • • Disturbs the land less than surface mining More expensive More hazardous for miners. Subsurface mining may be done – Underground shaft mines • Direct vertical shaft to the ore • Hoisted to the surface with buckets – Slope mines • Has a slanting passage • Ore hauled out by mine car Water Pollution • Runoff from mines may infiltrate waste material leaching (dissolving) trace elements and minerals • These leached minerals may be toxic, creating diseases in plants, animals, and people • May include Cadmium, Cobalt, Copper, Lead, Molybdenum, and Zinc • Specially constructed ponds may help contain some runoff but cannot eliminate the problem Water Pollution • Groundwater may also be impacted by mining operations • Impacted water infiltrating into the subsurface may collect as the groundwater • Groundwater can flow into other areas or seep into rivers and impact surface water bodies • Groundwater reclamation and remediation is very difficult and expensive Air Pollution • Smelting releases enormous amounts of pollutants into the atmosphere • Dust may also be released, affecting air quality • Scrubbers may be emplaced to limit air impact but these are expensive Biologic Impact • Direct impact includes the deaths of plants, animals, and people caused by mining activity • Indirect impacts include – Changes in nutrient cycling – Changes in species diversity – Changes in ecosystem stability Social Impact • Rapid influx of workers into an area unprepared for growth • Stress placed on local services • Land use changes from rural to urban – Affects water drainage (increased hardtop) – Increased air pollution – Disrupts ecological balance Minimizing Impact • Requires examination of the entire cycle • Environmental regulation that addresses problems such as water, air and sediment pollution resulting from all aspects of the mining operation • Onsite and offsite treatment of waste • Practicing the three R’s of waste management – Reduce the amount of waste produced – Reuse materials as much as possible – Maximize recycling